The current technology uses a 8.2 MHz high frequency signal source to create a magnetic field in a bandwidth sufficient enough to match the design tolerance of the disposable targets which are built to resonant at a single frequency. The base technology of detection and deactivation has been the same for almost two decades and has reached a defacto-standard worldwide. This technology is based on the need to sell a recurring consumable to the customer in the form of a target placed on merchandize that can be detected by a security system at the perimeter of a protected area with some type of alarm that will notify store personnel if the target has not had its physical characteristics changed by a deactivated, usually integrated into a point of sale (POS) area.
The current technology makes use of an 8.2 MHz (+/− about 4%) resonant target which is either disposable in the form of a label, or of a plastic enclosure with some type of re-attachment method to the merchandise. The disposable target is in the form of paper like label and has a mechanism by which either the inductor or the capacitor can be disabled. The reusable target is in the form of a discreet purchased capacitor and manufactured coil inductor with no method of altering either of these physical properties.
Currently, there are two distinct methods of detecting targets. Both methods operate by imposing a forcing function at a range of frequencies on a closed loop wire antenna structure to induce a near magnetic (H) field. This field impinges upon the inductor of the target when the target is close (e.g., within several feet) of the antenna structure. The impinged field causes a current to flow in the coil (inductor) which, when the frequency of the impinged field, and the resonant frequency of the target are close to one another, causes a sizable current/voltage (I/V) oscillation to be set up in the target.
In the first and most widely used methodology for detecting targets, referred to as the FM/AM or Swept method of detection, one gate is used as an FM transmitter and another is used as an AM receiver. The FM transmitter is used in continuous wave (CW) operation such that the receiver sees both the forced and the natural response of the target. This method is low cost, is excellent for aisle widths up to about four feet and uses low power (e.g., <100 μuV/m @ 30 m). The detection system of the receiver can either be logic based or digital signal processing (DSP) based. Systems near each other are RF slaved or use an offset sweeping rate (FM modulation) to avoid interference.
The second methodology for detecting targets, referred to as the pulsed detection or “pulse-listen” method, uses a pulsed transmitter coupled with a homodyne AM receiver as a single gate transceiver pair. The transmitter offers a random uniform distributed set of frequencies which transfers energy to the target. The AM receiver is gated to operate quickly after the transmitter pulse negative transition. The duty cycle of the transmitter is less than about 10% with a peak radiated power of less than about 1000 μV/m @ 30 m. The receiver only responds to the natural function and is exclusively a digital signal processor (DSP) based detection system. Systems physically close to each other (e.g., closer than about 5 m) need to be synchronized to each other in order to avoid interference. Variations of the transmitter pulse mask have a modulation level (e.g., pulse) being less than 100% to allow for a continuous wave (CW) component to be generated. Other than power dissipation increases, this variation has no effect on the system.
A known system of deactivation is very similar to that of the second pulse transmitter type of sensors. The method operates on one of three principles, either always on with no receiver; on at low power, detect and alarm, and switch to high power; or on at high power, and detect and alarm if not destroyed. The frequency band of operation is the same at that of the sensors. Peak power output is less than about 1000 μV/m @ 30 m. This is the current limit set by the Federal Communications Commission (FCC) and is about 8 dB below the European Conformity (CE) limit in Europe.
Deactivation of the target is almost immediate, depending upon where the transmitter is operating in the frequency cycle. Interfacing with the POS system is provided through an interlock input which causes the transmitter to operate when a closer (optical or electrical) signal is received from the POS system. Various styles and types of antenna can be integrated with the POS system either fixed (e.g., in a counter) or portable (e.g., handheld).
The current technology has been installed in hundreds of thousands of various installations throughout the world. Several issues have been recurring with each of the technologies for the various functions (targets, sensors and deactivators). First, it must be understood that the method of system operation is not a communications system as understood in the conventional sense. The system is actually a field disturbance function which operates in an unlicensed, and unregulated (for interference) band throughout the world. For example, in EAS systems of the RF type, a transmitter functions to generate energy at a predetermined frequency which is transmitted through the transmitter antenna to establish an electromagnetic field within a surveillance zone. Typically, because of manufacturing tolerances within security tags, transmitters generate energy which is continually swept up and down within a predetermined detection frequency range both above and below a selected center frequency at a predetermined sweep frequency rate. For example, if the desired center or tag frequency to be transmitted is 8.2 MHz, the transmitter may continually sweep up and down from about 7.5 MHz to 9.0 MHz at a sweep frequency rate between 60-90 Hz.
Various standard RF noise calculations, environmental models and system simulations are not applicable to predicting real-world operation in an absolute sense. The best that can be achieved with these methods is overall system design functions. The current EAS technology limits itself in several areas. Performance is predicated on an “average” noise environment and is based upon the most common target size and signal strength. Though highly adaptable and well filtered, the system is vulnerable to environmental resonances (door frames, ceiling wiring, etc.) and therefore in practice needs to have highly trained field service technicians solve these resonances.
Reliability of system operation and quality of service (QoS) in the known EAS industry are lacking, generally because the systems are not operated on truly robust communication systems and functionality. RF has as its major issue alarm integrity, and AM has target deactivation. Both of these problems contribute to cause customers' target purchases to decline year-to-year, even when their merchandise volume grows.
A major improvement in quality of RF alarm integrity came with U.S. Pat. No. 5,510,769 to Kajfez, et al. (hereinafter “Kajfez”), the contents of which are incorporated by reference herein in its entirety. Kajfez discloses an EAS system that detects tags having two resonant frequencies critically coupled to each other. This provided an approach for utilizing the two critically coupled resonant circuits within the 7.5-9.0 MHz swept pass band of the EAS system. The system in Kajfez requires a distinct relationship between the two resonant frequencies creating a known phase amplitude relationship between the tags. While a tag in Kajfez improved the detection reliability of the prior EAS systems, the Kajfez system has its limitations. First, any perturbation of the two signals-destroys the system. That is, if one of the two signals from a tag in Kajfez is not detected, the system does not recognize the tag, which renders the system ineffective for its intended purpose. Thus the system is not immune to localized tagging effects, such as, for example, being put near metal in shopping carts, etc. Second, the Kajfez tag is formed by two resonant circuits that must be overlaid with a critical manufactured coupling between the two circuits. In other words, the Kajfez tag is actually two EAS tags manufactured and overlaid on each other, which greatly increases the cost of the target. Third, Kajfez is limited to operation with a swept type EAS system only. That is, in order to get a response of a Kajfez tag, the EAS system must sweep through the tag. In other words, the Kajfez system must have a continuous signal that electromagnetically is not discontinuous, meaning it's always on; and it changes frequency and goes through and scans through the tag to get the response.
RFID technology is looked upon as a solution for the above identified problems; however that will likely not prove to be true. First, target prices are expensive, and will likely stay that way for the foreseeable future due to the high relative cost of silicon and wafer to target (e.g., antenna) attachment process costs. Second, EAS provides a perimeter, or corral type function. While RFID can simulate this function, aisle widths for high frequency (UHF)-RFID are typically too narrow at less than one meter using 2″×2″ size targets, and for ultra high frequency (UHF)-RFID systems are too unreliable (e.g., body and conductive structure detuning and target to antenna orientation) due to the physics of the RF medium employed. Therefore, RFID alone is not yet the saving grace of EAS, since it has too many technical and financial limitations for the foreseeable future.
The use of EAS (electronic article surveillance) tags and RFID (radio frequency identification) tags for a wide variety of read, track and/or detect applications is rapidly expanding. A smooth bridge between existing EAS and RFID functionality has been a consistent theme identified by users interested in RFID to allow them to obtain the benefits of RFID while maintaining their investment in EAS technology and its usefulness in protecting lower cost objects for sale that cannot justify the higher implementation cost of RFID. However, where identification tags are capable of receiving both EAS and RFID frequencies, the conventional manner in which the respective EAS or RFID signals return from these tags is processed exhibits certain shortcomings or limitations. For example, the reader for these signals comprises an 8.2 MHz EAS transceiver and a 13.56 MHz RFID transceiver in the same package that drives separate antennae via time domain switching between the two frequencies. The interference between the two technologies is handled by traditional analog signal filtering techniques. Utilizing such a configuration though, is challenging as it involves redundancy of components (i.e., duplication of transceiver components, duplication of antennae, etc.). In addition, the degree of filtering required for such a configuration is great (estimated at 100 dB) due to the very close proximity in frequency (less than 1 octave) and the relative signal amplitude differences allowable for the 2 transmission bands. Moreover, the need for two antenna for this configuration results in a much wider structure (e.g., roughly double) than for either technology deployed alone.
Even with these techniques, performance is inferior than for either technology deployed alone. The identification tag used in this related art EAS and RFID configuration includes two circuits: an RFID circuit and an EAS circuit, which are not coupled and have nothing to do with each other electro-magnetically. As noted above, the system uses time domain switching, via time division multiplex (TDM), between an RFID frequency and an EAS frequency to function as a system for both. However, by switching back and forth between RFID and EAS, the combined system by definition can not provide as much processing as single stand-alone RFID and EAS systems. Therefore the combined system is not complementary and will not operate as well as either single technology systems, at least because the time switching has a trade-off of less individual processing.
Traditionally, “pulse-listen” methodologies (e.g., transmitting a sequence of RF burst signals at different frequencies so that at least one of the frequencies bursts falls near a resonant frequency of the EAS tag) have been used in EAS but not RFID technologies, because the RFID chip requires a continuous signal emission from the reader to power the IC of the RFID tag. It would be beneficial to provide a system and method that can simultaneously detect EAS and RFID identification tag signals while avoiding the shortcomings discussed previously.